Design and investigation of scalable multicast recursive protocols for wired and wireless ad hoc networks

SEM has a major problem in the join/leave latency because or reconstruction of tree in case
of member leaving.

4.2 Overview of proposed protocol

The proposed Scalable Recursive Multicast protocol (SReM) uses a method that builds the
multicast tree dynamically and gradually as group members’ join/leave.

The proposed protocol introduces the idea of using a dynamic branching node-based
multicast tree (DBT) to deliver packets. In SReM, there are two types of signalling messages,
i.e., join/leave signalling messages (JS/JL) and branching node messages (BNMs). Each
receiver that wants to join/leave a multicast group (G) sends a join/leave message
(JoinM/LeavM) to its local multicast router (LMR) using IGMPv.3 [36]. This LMR then
sends a registration request message (RqM) to the multicast source (S) on behalf of this
receiver. In response to the receiving of the RqM, the source will send a registration replying
message (RpM) to confirm the registration. In the initial stage of the multicast tree setup, the
multicast source will be responsible of searching for the first branching node router (BNR)
by using of a pair of BNMs upon receiving these registration messages. Following that both
the multicast source and BNRs will perform this function (searching for BNRs).

As a result, a dynamic branching node-based multicast tree (DBT) will then be created. Each
of BNRs in DBT has a multicast forward table (MFT) with the multicast tree identity (MTI)
of (S,G), MFT includes the address of its previous BNR as well as a list of its next branching
nodes’ addresses. Using the DBT, SReM delivers multicast via BNRs by unicast.

As mentioned, SReM uses the mechanism of building the tree in response of join/leave of
receivers. This mechanism is similar to SEM [11], but in SEM the tree is build in advance.
SReM uses unicast mechanism to forward multicast data packets similar to REUNITE [65]
and HBH [22] but using only one multicast table in the branching nodes (MFT) without
using the multicast control table (MCT). SReM adapts a pair (S,G) to identify each group
similar to EXPRESS [37], but keeping the multicast state about their next BNRs rather than
the whole multicast group members.

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